单项选择题
A.turning ability deteriorates B.virtual mass increases C.the effect of the propeller transverse thrust on yaw alters D.the ship will turn with its head towards the wind
Sometimes lights are（）by fog，haze，dust，smoke，or precipi...
单项选择题Sometimes lights are（）by fog，haze，dust，smoke，or precipitation which may be present at the light，or between the light and the observer，and which is possibly unknown by the observer.
A.obscured B.darkened C.greyed D.delighted
Pilotage in this country is（）.A.Free of chargeB.Importa...
单项选择题Pilotage in this country is（）.
A.Free of charge B.Important C.Required D.Unnecessary
Mariners should ensure correct（）of aids to navigation d...
单项选择题Mariners should ensure correct（）of aids to navigation during twilight periods when some lighted aids to navigation are lit while others are not.
A.identification B.distinction C.discrimination D.clearly seeing
